Vinyl chloride-based polymer is homopolymer of vinyl chloride or copolymer containing 50% or more of vinyl chloride, wherein it has various application fields due to inexpensive, easy to control hardness, and applicable in most processing apparatuses. Furthermore, the vinyl chloride-based polymers may provide molding articles having excellent physical and chemical properties, such as mechanical strength, weather resistance, chemical resistance, and thus, have been widely used in various fields. However, since the vinyl chloride-based polymer by itself has low molding processability per se, various additives, such as a plasticizer and the like, are properly added to provide processability.
In related arts, as a method for improving the processability of vinyl chloride-based polymer, a method for improving the processability of vinyl chloride-based polymer itself by using a dispersion stabilizer such as polyvinyl alcohol during polymerization of vinyl chloride-based polymer was proposed. However, according to the above-mentioned method, there was a limitation in that the bulk specific gravity of the vinyl chloride-based polymer was increased, but the fusion processability of the polymer was decreased.
Accordingly, as a method for improving both the processability and the fusion property of vinyl chloride-based polymers, a method of adjusting a polymerization degree distribution property by changing a temperature during polymerization reaction of the vinyl chloride-based polymers was proposed. However, according to the above-mentioned methods, although vinyl chloride-based polymers having a high bulk density and improved processability may be prepared, the polymerization reaction time is increased and productivity is thereby decreased. In addition, due to a side reaction between reaction products such as vinyl chloride-based monomer and additives in response to a change in polymerization temperatures, there were limitations of decrease in the own material property characteristics of the polymers such as increase in coloration properties and decrease in mechanical properties.
As another method for improving the processability of vinyl chloride-based polymers, a method, in which a plasticizer is used together with the vinyl chloride-based polymers when a molding article is manufactured, has been mainly used. However, when the plasticizer is used as such, there is a problem in that the plasticizer moves to the surface of a product, and sticking thereby occurs on the surface, and plasticity gradually decreases as time goes by. In particular, phthalate plasticizers which are mainly used have limitations of exhibiting flexibility at substantially high temperatures, and requiring high energy during processing.
In particular, the vinyl chloride-based polymer having a high polymerization degree has a long fusion time and thereby has a limitation of remarkable decrease in productivity of processed molding article. When a processing temperature is raised to solve this, discoloration occurs due to structural properties of vinyl chloride-based polymers. In addition, when a plasticizer is added during processing, the processing may be performed at a low temperature, but there is a concern about decreasing the material property of a processed molding article, and therefore, a use amount is restricted.
Thus, a method for manufacturing vinyl chloride-based polymers capable of preparing high-polymerization-degree vinyl chloride-based polymers having excellent fusion proccessability with excellent polymerization productivity is required to be developed.